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The Performance‐Determining Role of Lewis Bases in Dye‐Sensitized Solar Cells Employing Copper‐Bisphenanthroline Redox Mediators
Author(s) -
Fürer Sebastian O.,
Milhuisen Rebecca A.,
Kashif Muhammad K.,
Raga Sonia R.,
Acharya Shravan S.,
Forsyth Craig,
Liu Maning,
Frazer Laszlo,
Duffy Noel W.,
Ohlin C. André,
Funston Alison M.,
Tachibana Yasuhiro,
Bach Udo
Publication year - 2020
Publication title -
advanced energy materials
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 10.08
H-Index - 220
eISSN - 1614-6840
pISSN - 1614-6832
DOI - 10.1002/aenm.202002067
Subject(s) - dye sensitized solar cell , redox , solar cell , copper , phenanthroline , lewis acids and bases , ligand (biochemistry) , coordination complex , pyridine , electrolyte , materials science , inorganic chemistry , chemistry , combinatorial chemistry , photochemistry , electrode , catalysis , medicinal chemistry , organic chemistry , metal , biochemistry , receptor , optoelectronics
Copper redox mediators have enabled open‐circuit voltages ( V OC ) of over 1.0 V in dye‐sensitized solar cells (DSCs) and have helped to establish DSCs as the most promising solar cell technology in low‐light conditions. The addition of additives such as 4‐ tert ‐butylpyridine (tBP) to these electrolytes has helped in achieving high solar cell performances. However, emerging evidence suggests that tBP coordinates to the Cu(II) species and limits the performance of these electrolytes. To date, the implications of this coordination are poorly understood. Here, the importance of Lewis base additives for the successful implementation of copper complexes as redox mediators in DSCs is demonstrated. Two redox couples, [Cu(dmp) 2 ] +/2+ and [Cu(dpp) 2 ] +/2+ (with dmp = 2,9‐dimethyl‐1,10‐phenanthroline and dpp = 2,9‐diphenyl‐1,10‐phenanthroline) in combination with three different Lewis bases, TFMP (4‐(trifluoromethyl)pyridine), tBP, and NMBI (1‐methyl‐benzimidazole), are considered. Through single‐crystal X‐ray diffraction analysis, absorption, and 1 H‐NMR spectroscopies, the coordination of Lewis bases to the Cu(II) centers are studied. This coordination efficiently suppresses recombination losses and is crucial for high performing solar cells. If, however, the coordination involves a ligand exchange, as is the case for [Cu(dpp) 2 ] +/2+ , the redox mediator regeneration at the counter electrode is significantly retarded and the solar cells show current limitations.